"And now for something completely different..."

andre kesteloot andre.kesteloot at verizon.net
Tue Feb 16 10:28:45 CST 2010

Bob Bruhns wrote:
> In the old days, there were a few other alternatives to plate modulation that did get reasonably good efficiency.  One was called
> AmpliPhase, it belonged to RCA and it combined two oppositely phase-modulated output stages. [...] Ampli-Phase
> was commercially viable, and some stations used it.  The inherent linearity of the Terman-Woodyard and Taylor systems were not so
> good, but I understand that with enough negative feedback, they were OK.
> The problem with those systems was complexity, and adjustment was difficult, and multi-frequency operation was tricky. That was an
> issue with the old Conelrad requirements for stations to be able to transmit on 640 KHz or 1240 KHz, and also on shortwave where a
> transmitter might be expected to change bands a few times a day.  

I am somewhat familiar with Ampliphase transmitters. The Conelrad 
regulations did not apply overseas and medium-wave transmitters were 
easy to adjust, and the lower power consumption made it easier on 
ventilation (or A/C) requirements (not to mention the electric bill).
For short-wave operation, tuning, unfortunately, was not quite as 
simple; as the transmitting station usually has to switch from one 
frequency to an other (and one short-wave band to another) in a very 
short time.


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